1. Field Of The Invention
This invention relates to a signal recording device which is represented typically by an R-DAT (rotary head-digital audio tapedeck).
2. Background Art
In an R-DAT or the like, an analog audio signal, which is a recording signal, is converted from analog-to-digital (A/D) form so that it is recorded in the form of a digital signal on the magnetic tape. In the quantization of an analog signal, a quantizing distortion occurs. Hitherto, a dither signal is used as a random noise to eliminate the quantizing distortion.
FIG. 1 is a block diagram showing a signal recording device in which a signal is recorded with the dither signal. In FIG. 1, an analog audio signal is applied to an input terminal. A digital noise generating circuit 6 generates digital noise as the dither signal. The digital noise generated by the noise generating circuit 6 is subjected to D/A (digital-to-analog) conversion in a D/A converter circuit 7. The output of the D/A circuit 7 is applied to an addition circuit 2 where it is added to the analog audio signal. The output of the addition circuit 2 is applied to an A/D converter circuit 3, where it is subjected to A/D conversion. The output of the A/D converter circuit 3 is applied to a subtraction circuit 4.
The digital noise generated by the digital noise generating circuit 6, after being delayed for a predetermined period of time by a delay circuit 8 (corresponding to the sum of delay times in the D/A converter circuit 7, the addition circuit 2 and the A/D converter circuit 3), is applied to the subtraction circuit 4. In the subtraction circuit 4, the digital noise is subtracted from the output signal of the A/D converter circuit 3 and the result of subtraction is provided at its output terminal 5. The signal thus provided at the output terminal 5 is applied to the rotary head so as to be recorded on the magnetic tape.
In the above-described method, the recording signal is added to the dither signal before being subjected to A/D conversion and, therefore, the quantizing distortion can be decreased at the A/D conversion.
However, in the signal recording device thus organized, for sufficient effect it is essential that the A/D converter circuit 3 and the D/A converter circuit 7 are uniform in accuracy and in quantization characteristic. Furthermore, if the frequency of the digital noise is set in the audio frequency band, then the S/N ratio is lowered.